In mobile communication networks, especially LTE (long term evolution), TD-LTE (also known as LTE TDD (time division duplex)) is a standard that may be used. In TD-LTE, until now, there are several predefined UL/DL configurations. Uplink-downlink configurations with both 5 ms and 10 ms downlink-to-uplink switch-point periodicity are supported. In case of 5 ms downlink-to-uplink switch-point periodicity, a special switching subframe exists in both half-frames. In case of 10 ms downlink-to-uplink switch-point periodicity, the special subframe exists in the first half-frame only. The ratio of DL throughput to UL throughput could be adjusted by using different UL/DL configurations which is one of the advantages of the TDD mode. Practically, the UL/DL configuration is predetermined by the operator and should be set in coordination all through the whole network for interference issues.
LTE-Advanced, an evolved version of LTE, with bandwidths up to 100 MHz is currently under study to fulfill the targets defined in TR 36.913 (“Requirements for further advancements for E-UTRA/LTE-Advanced”). Here, the 100 MHz system bandwidth may be achieved via aggregation of individual component carriers (CCs). Each component carrier can be limited in bandwidth to 20 MHz. A terminal may simultaneously receive or transmit one or multiple component carriers depending on its capabilities. In some initial discussion, the L1 specification may support carrier aggregation for both contiguous and non-contiguous component carriers. Aggregation of non-contiguous component carriers means the component carriers are either non-adjacent to each other on the same frequency band, or even in totally different frequency bands.
In TDD mode of LTE-A (i.e. TD-LTE-A), the same technology of carrier aggregation can be utilized to improve the capacity and to keep compatible with LTE Rel-8 TDD terminals.
Compared with FDD system, which always has transmission opportunity for both downlink and uplink, the TDD system could only alternate between downlink and uplink transmissions.
Thus, in LTE Advanced system for TDD (time division duplex) or TD-LTE, the available bandwidth can be extended by the means of carrier aggregation. The round trip time (RTT) of HARQ cannot be decreased as it is particularly caused by the TDD UL/DL (uplink, downlink) configuration.
There may be a need for providing an efficient method for scheduling a communication link, which may reduce the round trip time of the end-to-end traffic in TD-LTE-A system for delay sensitive services such as VoIP or real-time gaming.